The present invention relates to a process for the polymerisation and copolymerisation of 1-olefins, and particularly to a process for transitioning between different polymerization catalyst systems.
During the production of olefin polymers in a commercial reactor it is often necessary to transition from one type of catalyst system producing polymers having certain properties and characteristics to another catalyst system capable of producing polymers of different chemical and/or physical attributes. Transitioning between similar traditional Ziegler-Natta type catalysts for example, or compatible catalysts, generally takes place easily. However, where the catalysts are incompatible or of different types the process is typically complicated. For example, transitioning between a traditional Ziegler-Natta type catalyst and chromium based catalyst, two incompatible catalysts, it has been found that some of the components of the traditional Ziegler catalyst or the cocatalyst/activator act as poisons to the chromium based catalyst. Consequently, these poisons prevent the chromium catalyst from promoting polymerization. In another example, the extreme different responses to molecular weight regulators, such as hydrogen and comonomer, of traditional Ziegler-Natta catalysts and metallocene catalysts makes these catalysts incompatible. Any traces of active Ziegler-Natta catalyst will produce very high molecular weight product under metallocene catalyst reactor conditions. Furthermore, particularly in a continuous transitioning process, the interaction between the two incompatible catalysts may lead to production of high levels of small particles less than about 100 microns, termed fines. These fines can induce operability problems in the reactor such as fouling and sheeting.
In known transitioning techniques, to accomplish an effective transition between incompatible catalysts, the first catalyzed olefin polymerization process is stopped by various techniques known in the art. For example in reactions involving use of chromium based catalysts, oxygen, CO, water or polar hydrocarbons such as alcohols, ethers, ketones and aldehydes are known to be effective in reaction termination. The reactor is then emptied, recharged and a second catalyst is introduced into a reactor. Such catalyst conversions are time consuming and costly because of the need for a reactor shut-down for an extended period of time during transition.
WO 99/12981 discloses that ethylene and other 1-olefins may be polymerised by contacting it with certain late transition metal complexes of selected 2,6-pyridinecarboxaldehydebis (imines) and 2,6-diacylpyridinebis (imines).
EP-A-751965 discloses methods of transitioning between incompatible catalysts, involving the use of catalyst killers. It defines xe2x80x9cincompatiblexe2x80x9d catalysts as those which satisfy one or more of the following criteria: 1) those catalysts that in each other""s presence reduce the activity of at least one of the catalysts by greater than 50%; 2) those catalysts such that under the same reactive conditions one of the catalysts produces polymers having a molecular weight greater than two times higher than any other catalyst in the system; and 3) those catalysts that differ in comonomer incorporation or reactivity ratio under the same conditions by more than about 30%.
According to the above definition, late transition metal catalysts such as the above-mentioned 2,6-pyridinecarboxaldehydebis(imine) type catalysts are incompatible with most known types of catalysts. For example, 2,6-pyridinecarboxaldehydebis(imine) type catalysts typically exhibit a very low comonomer incorporation or reactivity ratio compared with other catalyst types. Accordingly it would be expected that transitioning from one to the other would require procedures such as those described above for incompatible catalysts, with all the attendant disadvantages.
We have surprisingly discovered however that it is possible to transition between late transition metal catalysts and catalysts which are incompatible according to the above definition without the need for such procedures.
Accordingly in a first aspect the present invention provides a process for the polymerisation and copolymerisation of 1-olefins in which a transition is made between two catalysts, comprising the steps of
a) discontinuing the feed of the first catalyst into the polymerization reactor, and then
b) introducing the second catalyst into the reactor,
wherein one of the catalysts comprises a late transition metal catalyst and the other is a catalyst which is incompatible therewith.
Preferably the transition is effected by introducing the second catalyst without first eliminating all activity of the first catalyst and/or without first removing all traces of the first catalyst. More preferably, no deactivating agent (catalyst killer) is used.
In an alternative embodiment, subsequent to step a) a deactivating agent in a sufficient amount to deactivate the first catalyst is introduced into the reactor before the second catalyst is introduced into the reactor.
By xe2x80x9clate transition metal catalystxe2x80x9d (hereinafter LTM catalyst) is meant a catalyst comprising a complex of a metal from Groups VIIIb or Ib of the Periodic Table.
By xe2x80x9cincompatiblexe2x80x9d is meant the definition previously given: namely that the two catalysts satisfy at least one of the following conditions: 1) catalysts which in each other""s presence reduce the activity of at least one of the catalysts by greater than 50%; 2) under the same reactive conditions one of the catalysts produces polymers having a molecular weight two times or more that of any other catalyst in the system; and 3) catalysts that differ in comonomer incorporation or reactivity ratio under the same conditions by more than 30%.
Catalysts which are incompatible with the LTM catalysts includes Phillips type (chromium) catalysts, metallocene catalysts and Ziegler-Natta catalysts. However this invention also includes within its scope the case where two LTM catalysts are incompatible with each other according to the above definition.
Preferably the LTM catalyst comprises a complex of the formula 
wherein M is Fe[II], Fe[III], Co[II], Co[III], Ni[II], Rh[II], Rh[III], Ru[II], Ru[III], Ru[IV] or Pd[II]; X represents an atom or group covalently or ionically bonded to the transition metal M; T is the oxidation state of the transition metal M and b is the valency of the atom or group X; L is a group datively bound to M, and n is from 0 to 5; A1 to A3 are each independently N or P or CR, with the proviso that at least one is CR; and R and R4 to R7 are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiRxe2x80x23 where each Rxe2x80x2 is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl.
A typical Phillips type catalyst employs a combination of a support material to which has first been added a chromium-containing material wherein at least part of the chromium is in the hexavalent state by heating in the presence of molecular oxygen. The support is generally composed of about 80 to 100 wt. % silica, the remainder, if any, being selected from the group consisting of refractory metal oxides, such as aluminium, boria, magnesia, thoria, zirconia, titania and mixtures of two or more of these refractory metal oxides. Supports can also comprise alumina, aluminium phosphate, boron phosphate and mixtures thereof with each other or with silica.
The chromium compound is typically added to the support as a chromium (III) compound such as the acetate or acetylacetonate in order to avoid the toxicity of chromium (VI). The raw catalyst is then calcined in air at a temperature between 250 and 1000xc2x0 C. for a period of from a few seconds to several hours. This converts at least part of the chromium to the hexavalent state. Reduction of the Cr VI to its active form normally occurs in the polymerisation reaction, but can be done at the end of the calcination cycle with CO at about 350xc2x0 C.
Fluorine, aluminium and/or titanium may be added to the raw Phillips catalyst to modify it.
Metallocenes may typically be represented by the general formula:
(C5Rn)yZx(C5Rm) M L(4xe2x88x92yxe2x88x921)
where (C5Rx)n and (C5Rm) are cyclopentadienyl ligands,
R is hydrogen, alkyl, aryl, alkenyl, etc.
M is a Group IVA metal
Z is a bridging group,
L is an anionic ligand, and
y is 0,1 or 2, n and m are from 1 to 5, x is 0 or 1.
The most preferred complexes are those wherein y is 1 and L is halide or alkyl. Typical examples of such complexes are bis(cyclopentadienyl)zirconium dichloride and bis(cyclopentadienyl zirconium dimethyl. In such metallocene complexes the cyclopentadienyl ligands may suitably be substituted by alkyl groups such as methyl, n-butyl or vinyl. Alternatively the R groups may be joined together to form a ring substituent, for example indenyl or fluorenyl. The cyclopentadienyl ligands may be the same or different. Typical examples of such complexes are bis(n-butylcyclopentadienyl)zirconium dichloride or bis(methylcyclopentadienyl)zirconium dichloride.
Further examples of metallocene complexes are those wherein the anionic ligand represented in the above formula is replaced with a diene moiety. In such complexes the transition metal may be in the +2 or +4 oxidation state and a typical example of this type of complex is ethylene bis indenyl zirconium (II) 1,4-diphenyl butadiene. Examples of such complexes may be found in EP 775148A the disclosure of which is incorporated herein by reference.
Ziegler-Natta catalysts, in general, consist of two main components. One component is an alky or hydride of a Group I to III metal, most commonly Al(Et)3 or Al(iBu)3 or Al(Et)2Cl but also encompassing Grignard reagents, n-butyllithium, or dialkylzinc compounds. The second component is a salt of a Group IV to VIII transition metal, most commonly halides of titanium or vanadium such as TiCl4, TiCl3, VCl4, or VOCl3. The catalyst components when mixed, usually in a hydrocarbon solvent, may form a homogeneous or heterogeneous product. Such catalysts may be impregnated on a support, if desired, by means known to those skilled in the art and so used in any of the major processes known for co-ordination catalysis of polyolefins such as solution, slurry, and gas-phase. In addition to the two major components described above, minor amounts of other compounds (typically electron donors) may be added to further modify the polymerisation behaviour or activity of the catalyst. A wide variety of monomers may thus be polymerised by Ziegler-Natta catalysts. Depending on the particular components used, and the specific method of combination, it is possible to produce catalysts which are very effective for the polymerisation and copolymerisation of ethylene, dienes, and higher alpha-olefins. Particularly important applications for Ziegler-Natta catalysts are for the manufacture of high molecular weight ethylene copolymers and isotactic polypropylene.
It will be understood that the transitioning process of the invention can be performed in either directionxe2x80x94i.e. from the LTM catalyst to the other catalyst or vice versa. Furthermore, it will be understood that whilst it is not in fact necessary to take any action to address the activity/presence of the first catalyst before adding the second, it is within the scope of the invention to reduce or eliminate the activity of the first catalyst and/or to remove at least part of the catalyst. For example, the activity of the first catalyst may be reduced by up to 30% from its maximum prior to addition of the second catalyst, or alternatively by up to 50, 70 or by at least 95%, or it may be killed completely. For reducing activity, known catalyst inhibitors or poisons such as oxygen, water, ammonia, carbon monoxide, carbon dioxide, alcohols and ketones may be used. Partial reduction in activity of the first catalyst may also for example be achieved by continuing polymerisation for a certain period of time (for example between 5 minutes and 12 hours) after having discontinued introduction of the first catalyst and/or any associated co-catalyst, before commencing introduction of the second catalyst and/or its associated co-catalyst.
After introduction of the first catalyst has been discontinued, the polymerisation reactor may be partially or completely emptied. Completely emptying the reactor ensures that when the second catalyst is introduced, all the polymer subsequently produced is purely that derived from the second catalyst. However it is preferred at most only to partially empty the reactor, e.g. by reducing the bed height in the case of a gas phase fluidised bed reactor, as this is less disruptive of the polymerisation process. Although this results in the polymerisation with the second catalyst initially producing polymer which is mixed with polymer derived from the first catalyst, this is a relatively minor problem in the case of the present invention, because one of the catalysts is a late transition metal catalyst. Typically, between zero and half of the contents of the reactor by volume may be removed, though preferably only one third or less are removed. In the most preferred case, none of the contents of the reactor are removed prior to commencing the polymerisation with the second catalyst.
When transitioning from a first to a second catalyst the usual initial step is to discontinue the catalyst feed. If desired, the polymerisation reactor may then be partially or completely emptied, as discussed above. The new catalyst is then introduced and, if necessary, the reactor conditions are adapted to the conditions required by the new catalyst. For example, in the case of transition from a chromium catalyst when the reactor is not completely emptied, the transition is followed by IR measurements on the produced polymer to determine when the system is free from any chromium-based polymer, i.e. to determine when the produced polymer is within the LTM polymer specifications. The transition can also be followed by melt index measurements of the produced polymer.
The specific reactor conditions during transition depend inter alia on catalyst activity, type and amount of comonomer, type of polymer to be produced, and the production equipment. Consequently, they have to be determined for each specific product in a particular plant. For example, in general the reactor conditions when using metallocene catalysts include a reduced feed of comonomer because the comonomers are much more readily incorporated in metallocene catalyzed polymers than in LTM catalysed polymers of equal polymer density. The melt flow index is corrected by introducing hydrogen, and also, to a certain degree, ethylene.
A particularly favoured transition is that between 2,6-pyridinecarboxaldehydebis(imine) type catalysts comprising complexes of the formula (I) as defined above, and chromium catalysts.
It is preferred that the process of the invention is carried out in slurry or gas phase.
In the complexes of Formula (I) it is preferred that A1 to A3 are each independently CR where each R is as defined above. In alternative preferred embodiments, A1 and A3 are both N and A2 is CR, or one of A1 to A3 is N and the others are independently CR.
The group L may be an ether such as tetrahydrofuran or diethylether, and alcohol such as ethanol or butanol, a primary, secondary or tertiary amine, or a phosphine.
Preferred catalysts based on complexes of the Formula (I) comprise a complex having the formula 
wherein R1 to R7 are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiRxe2x80x23 where each Rxe2x80x2 is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl.
R5 and R7 are preferably independently selected from substituted or unsubstituted alicyclic, heterocyclic or aromatic groups, for example, phenyl, 1-naphthyl, 2-naphthyl, 2-methylphenyl, 2-ethylphenyl, 2,6-diisopropylphenyl, 2,3-diisopropylphenyl, 2,4-diisopropylphenyl, 2,6-di-n-butylphenyl, 2,6-dimethylphenyl, 2,3-dimethylphenyl, 2,4-dimethylphenyl, 2-t-butylphenyl, 2,6-diphenylphenyl, 2,4,6-trimethylphenyl, 2,6-trifluoromethylphenyl, 4-bromo-2,6-dimethylphenyl, 3,5 dichloro2,6-diethylphenyl, and 2,6,bis(2,6-dimethylphenyl)phenyl, cyclohexyl and pyridinyl.
In a preferred embodiment R5 is represented by the group xe2x80x9cPxe2x80x9d and R7 is represented by the group xe2x80x9cQxe2x80x9d as follows: 
wherein R19 to R28 are independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl; when any two or more of R1 to R4, R6 and R19 to R28 are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl, said two or more can be linked to form one or more cyclic substituents.
The ring systems P and Q are preferably independently 2,6-hydrocarbylphenyl or fused-ring polyaromatic, for example, 1-naphthyl, 2-naphthyl, 1-phenanthrenyl and 8-quinolinyl.
Preferably at least one of R19, R20, R21 and R22 is hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl. More preferably at least one of R19 and R20, and at least one of R21 and R22, is hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl. Most preferably R19, R20, R21 and R22 are all independently selected from hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl. R19, R20, R21 and R22 are preferably independently selected from methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert.-butyl, n-pentyl, neopentyl, n-hexyl, 4-methylpentyl, n-octyl, phenyl and benzyl.
R1, R2, R3, R4, R6, R19, R20, R21, R22, R23, R25, R26 and R28 are preferably independently selected from hydrogen and C1 to C8 hydrocarbyl, for example, methyl, ethyl, n-propyl, n-butyl, t-butyl, n-hexyl, n-octyl, phenyl and benzyl.
In an alternative embodiment R5 is a group having the formula xe2x80x94NR29R30 and R7 is a group having the formula xe2x80x94NR31R32, wherein R29 to R32 are independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl; when any two or more of R1 to R4, R6 and R29 to R32 are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl, said two or more can be linked to form one or more cyclic substituents.
Each of the atoms nitrogen atoms is coordinated to the metal by a xe2x80x9cdativexe2x80x9d bond, ie a bond formed by donation of a lone pair of electrons from the nitrogen atom. The remaining bonds on each of these atoms are covalent bonds formed by electron sharing between the atoms and the organic ligand as shown in the defined formula for the metal complex illustrated above.
The atom or group represented by X in the compounds of Formula (I) and (II) can be, for example, selected from halide, sulphate, nitrate, thiolate, thiocarboxylate, BF4xe2x88x92, PF6xe2x88x92, hydride, hydrocarbyloxide, carboxylate, hydrocarbyl, substituted hydrocarbyl and heterohydrocarbyl, or xcex2-diketonates. Examples of such atoms or groups are chloride, bromide, methyl, ethyl, propyl, butyl, octyl, decyl, phenyl, benzyl, methoxide, ethoxide, isopropoxide, tosylate, triflate, formate, acetate, phenoxide and benzoate. Preferred examples of the atom or group X in the compounds of Formula (I) are halide, for example, chloride, bromide; hydride; hydrocarbyloxide, for example, methoxide, ethoxide, isopropoxide, phenoxide; carboxylate, for example, formate, acetate, benzoate; hydrocarbyl, for example, methyl ethyl, propyl, butyl, octyl, decyl, phenyl, benzyl; substituted hydrocarbyl; heterohydrocarbyl; tosylate; and triflate. Preferably X is selected from halide, hydride and hydrocarbyl. Chloride is particularly preferred.
Preferred metals M in the complexes of Formula (I) are Fe and Co.
Preferred compounds of the Formula (I) include the following:
2,6-diacetylpyridinebis(2,6-diisopropylanil)FeCl2 
2,6-diacetylpyridine(2,6-diisopropylanil)CoCl2 
2,6-diacetylpyridinebis(2-tert.-butylanil)FeCl2 
2,6-diacetylpyridinebis(2,3-dimethylanil)FeCl2 
2,6-diacetylpyridinebis(2-methylanil)FeCl2 
2,6-diacetylpyridinebis(2,4-dimethylanil)FeCl2 
2,6-diacetylpyridinebis(2,6-dimethylanil)FeCl2 
2,6-diacetylpyridinebis(2,4,6 trimethyl anil)FeCl2 
2,6-dialdiminepyridinebis(2,6-dimethylanil)FeCl2 
2,6-dialdiminepytidinebis(2,6-diethylanil)FeCl2 
2,6-dialdiminepyridinebis(2,6-diisopropylanil)FeCl2 
2,6-dialdiminepyridinebis(1-naphthil)FeCl2 or
2,6-bis(1,1-diphenylhydrazone)pyridine FeCl2.
Each of the catalysts utilised in the present invention can if desired comprise more than one compound of that type. For example, the catalysts of Formula (I) can also include one or more other types of transition metal compounds or catalysts, for example, nitrogen containing catalysts such as those described in our copending applications WO 99/12981 or GB 9903402.7.
The complexes of formula (I) are generally used as catalysts in conjunction with activator compounds. Examples of such activator compounds include organoaluminium compounds and hydrocarbylboron compounds. Suitable organoaluminium compounds include compounds of the formula AlR3, where each R is independently C1-C12 alkyl or halo. Examples include trimethylaluminium (TMA), triethylaluminium (TEA), tri-isobutylaluminium (TIBA), tri-n-octylaluminium, methylaluminium dichloride, ethylaluminium dichloride, dimethylaluminium chloride, diethylaluminium chloride, ethylaluminiumsesquichloride, methylaluminiumsesquichloride, and alumoxanes. Alumoxanes are well known in the art as typically the oligomeric compounds which can be prepared by the controlled addition of water to an alkylaluminium compound, for example trimethylaluminium. Such compounds can be linear, cyclic or mixtures thereof. Commercially available alumoxanes are generally believed to be mixtures of linear and cyclic compounds. The cyclic alumoxanes can be represented by the formula [R16AlO]s and the linear alumoxanes by the formula R17(R18AlO)s wherein s is a number from about 2 to 50, and wherein R16, R17, and R18 represent hydrocarbyl groups, preferably C1 to C6 alkyl groups, for example methyl, ethyl or butyl groups. Alkylalumoxanes such as methylalumoxane (MAO) are preferred.
Mixtures of alkylalumoxanes and trialkylaluminium compounds are particularly preferred, such as MAO with TMA or TIBA. In this context it should be noted that the term xe2x80x9calkylalumoxanexe2x80x9d as used in this specification includes alkylalumoxanes available commercially which may contain a proportion, typically about 10 wt %, but optionally up to 50 wt %, of the corresponding trialkylaluminium; for instance, commercial MAO usually contains approximately 10 wt % trimethylaluminium (TMA), whilst commercial MMAO contains both TMA and TIBA. Quantities of alkylalumoxane quoted herein include such trialkylaluminium impurities, and accordingly quantities of trialkylaluminium compounds quoted herein are considered to comprise compounds of the formula AlR3 additional to any AlR3 compound incorporated within the alkylalumoxane when present.
Examples of suitable hydrocarbylboron compounds are boroxines, trimethylboron, triethylboron, dimethylphenylammoniumtetra(phenyl)borate, trityltetra(phenyl)borate, triphenylboron, dimethylphenylammonium tetra(pentafluorophenyl)borate, sodium tetrakis[(bis-3,5-trifluoromethyl)phenyl]borate, H+(OEt2)[(bis-3,5-trifluoromethyl)phenyl]borate, trityltetra(pentafluorophenyl)borate and tris(pentafluorophenyl)boron.
An alternative class of activators comprise salts of a cationic oxidising agent and a non-coordinating compatible anion. Examples of cationic oxidising agents include: ferrocenium, hydrocarbyl-substituted ferrocenium, Ag+, or Pb2+. Examples of non-coordinating compatible anions are BF4xe2x88x92, SbF6xe2x88x92, PF6xe2x88x92, tetrakis(phenyl)borate and tetrakis(pentafluorophenyl)borate.
The catalysts utilised in the present invention can be unsupported or supported on a support material, for example, silica, alumina, MgCl2 or zirconia, or on a polymer or prepolymer, for example polyethylene, polypropylene, polystyrene, or poly(aminostyrene).
The polymerisation conditions can be, for example, solution phase, slurry phase, gas phase or bulk phase, with polymerisation temperatures ranging from xe2x88x92100xc2x0 C. to +300xc2x0 C., and at pressures of atmospheric and above, particularly from 140 to 4100 kPa. If desired, the catalyst can be used to polymerise ethylene under high pressure/high temperature process conditions wherein the polymeric material forms as a melt in supercritical ethylene. Preferably the polymerisation is conducted under gas phase fluidised bed or stirred bed conditions.
Suitable monomers for use in the polymerisation process of the present invention are, for example, ethylene and C2-20 xcex1-olefins, specifically propylene, 1-butene, 1-pentene, 1-hexene, 4-methylpentene-1,1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, and 1-eicosene. Other monomers include methyl methacrylate, methyl acrylate, butyl acrylate, acrylonitrile, vinyl acetate, and styrene. Preferred monomers for homopolymerisation processes are ethylene and propylene.
The process of the invention can also be used for copolymerising ethylene or propylene with each other or with other 1-olefins such as 1-butene, 1-hexene, 4-methylpentene-1, and octene, or with other monomeric materials, for example, methyl methacrylate, methyl acrylate, butyl acrylate, acrylonitrile, vinyl acetate, and styrene.
Irrespective of the polymerisation or copolymerisation technique employed, polymerisation or copolymerisation is typically carried out under conditions that substantially exclude oxygen, water, and other materials that act as catalyst poisons. Also, polymerisation or copolymerisation can be carried out in the presence of additives to control polymer or copolymer molecular weights.
Slurry phase polymerisation conditions or gas phase polymerisation conditions are particularly useful for the production of high or low density grades of polyethylene, and polypropylene. In these processes the polymerisation conditions can be batch, continuous or semi-continuous. Furthermore, one or more reactors may be used, e.g. from two to five reactors in series. Different reaction conditions, such as different temperatures or hydrogen or comonomer concentrations may be employed in the different reactors. In the slurry phase process and the gas phase process, the catalyst is generally metered and transferred into the polymerisation zone in the form of a particulate solid either as a dry powder (e.g. with an inert gas) or as a slurry. This solid can be, for example, a solid catalyst system formed from the one or more of complexes of the invention and an activator with or without other types of catalysts, or can be the solid catalyst alone with or without other types of catalysts. In the latter situation, the activator can be fed to the polymerisation zone, for example as a solution, separately from or together with the solid catalyst. Preferably the catalyst system or the transition metal complex component of the catalyst system employed in the slurry polymerisation and gas phase polymerisation is supported on one or more support materials. Most preferably the catalyst system is supported on the support material prior to its introduction into the polymerisation zone. Suitable support materials are, for example, silica, alumina, zirconia, talc, kieselguhr, or magnesia. Impregnation of the support material can be carried out by conventional techniques, for example, by forming a solution or suspension of the catalyst components in a suitable diluent or solvent, and slurrying the support material therewith. The support material thus impregnated with catalyst can then be separated from the diluent for example, by filtration or evaporation techniques. Once the polymer product is discharged from the reactor, any associated and absorbed hydrocarbons are substantially removed, or degassed, from the polymer by, for example, pressure let-down or gas purging using fresh or recycled steam, nitrogen or light hydrocarbons (such as ethylene). Recovered gaseous or liquid hydrocarbons may be recycled to the polymerisation zone.
In the slurry phase polymerisation process the solid particles of catalyst, or supported catalyst, are fed to a polymerisation zone either as dry powder or as a slurry in the polymerisation diluent. The polymerisation diluent is compatible with the polymer(s) and catalyst(s), and may be an alkane such as hexane, heptane, isobutane, or a mixture of hydrocarbons or paraffins. Preferably the particles are fed to a polymerisation zone as a suspension in the polymerisation diluent. The polymerisation zone can be, for example, an autoclave or similar reaction vessel, or a continuous loop reactor, e.g. of the type well-know in the manufacture of polyethylene by the Phillips Process. When the polymerisation process of the present invention is carried out under slurry conditions the polymerisation is preferably carried out at a temperature above 0xc2x0 C., most preferably above 15xc2x0 C. The polymerisation temperature is preferably maintained below the temperature at which the polymer commences to soften or sinter in the presence of the polymerisation diluent. If the temperature is allowed to go above the latter temperature, fouling of the reactor can occur. Adjustment of the polymerisation within these defined temperature ranges can provide a useful means of controlling the average molecular weight of the produced polymer. A further useful means of controlling the molecular weight is to conduct the polymerisation in the presence of hydrogen gas which acts as chain transfer agent. Generally, the higher the concentration of hydrogen employed, the lower the average molecular weight of the produced polymer.
In bulk polymerisation processes, liquid monomer such as propylene is used as the polymerisation medium.
Methods for operating gas phase polymerisation processes are well known in the art. Such methods generally involve agitating (e.g. by stirring, vibrating or fluidising) a bed of catalyst, or a bed of the target polymer (i.e. polymer having the same or similar physical properties to that which it is desired to make in the polymerisation process) containing a catalyst, and feeding thereto a stream of monomer at least partially in the gaseous phase, under conditions such that at least part of the monomer polymerises in contact with the catalyst in the bed. The bed is generally cooled by the addition of cool gas (e.g. recycled gaseous monomer) and/or volatile liquid (e.g. a volatile inert hydrocarbon, or gaseous monomer which has been condensed to form a liquid). The polymer produced in, and isolated from, gas phase processes forms directly a solid in the polymerisation zone and is free from, or substantially free from liquid. As is well known to those skilled in the art, if any liquid is allowed to enter the polymerisation zone of a gas phase polymerisation process the quantity of liquid in the polymerisation zone is small in relation to the quantity of polymer present. This is in contrast to xe2x80x9csolution phasexe2x80x9d processes wherein the polymer is formed dissolved in a solvent, and xe2x80x9cslurry phasexe2x80x9d processes wherein the polymer forms as a suspension in a liquid diluent.
The gas phase process can be operated under batch, semi-batch, or so-called xe2x80x9ccontinuousxe2x80x9d conditions. It is preferred to operate under conditions such that monomer is continuously recycled to an agitated polymerisation zone containing polymerisation catalyst, make-up monomer being provided to replace polymerised monomer, and continuously or intermittently withdrawing produced polymer from the polymerisation zone at a rate comparable to the rate of formation of the polymer, fresh catalyst being added to the polymerisation zone to replace the catalyst withdrawn form the polymerisation zone with the produced polymer.
Methods for operating gas phase fluidised bed processes for making polyethylene, ethylene copolymers and polypropylene are well known in the art. The process can be operated, for example, in a vertical cylindrical reactor equipped with a perforated distribution plate to support the bed and to distribute the incoming fluidising gas stream through the bed. The fluidising gas circulating through the bed serves to remove the heat of polymerisation from the bed and to supply monomer for polymerisation in the bed. Thus the fluidising gas generally comprises the monomer(s) normally together with some inert gas (e.g. nitrogen or inert hydrocarbons such as methane, ethane, propane, butane, pentane or hexane) and optionally with hydrogen as molecular weight modifier. The hot fluidising gas emerging from the top of the bed is led optionally through a velocity reduction zone (this can be a cylindrical portion of the reactor having a wider diameter) and, if desired, a cyclone and or filters to disentrain fine solid particles from the gas stream. The hot gas is then led to a heat exchanger to remove at least part of the heat of polymerisation. Catalyst is preferably fed continuously or at regular intervals to the bed. At start up of the process, the bed comprises fluidisable polymer which is preferably similar to the target polymer. Polymer is produced continuously within the bed by the polymerisation of the monomer(s). Preferably means are provided to discharge polymer from the bed continuously or at regular intervals to maintain the fluidised bed at the desired height. The process is generally operated at relatively low pressure, for example, at 10 to 50 bars, and at temperatures for example, between 50 and 120xc2x0 C. The temperature of the bed is maintained below the sintering temperature of the fluidised polymer to avoid problems of agglomeration.
When using the catalysts of the present invention under gas phase polymerisation conditions, the catalyst, or one or more of the components employed to form the catalyst can, for example, be introduced into the polymerisation reaction zone in liquid form, for example, as a solution in an inert liquid diluent. Thus, for example, the transition metal component, or the activator component, or both of these components can be dissolved or slurried in a liquid diluent and fed to the polymerisation zone. Under these circumstances it is preferred the liquid containing the component(s) is sprayed as fine droplets into the polymerisation zone. The droplet diameter is preferably within the range 1 to 1000 microns. EP-A-0593083, the teaching of which is hereby incorporated into this specification, discloses a process for introducing a polymerisation catalyst into a gas phase polymerisation. The methods disclosed in EP-A-0593083 can be suitably employed in the polymerisation process of the present invention if desired.
The present invention is illustrated in the following Examples. The two catalysts used are incompatible according to category 2) of the previously mentioned definition, in that they have substantially differing HLMI.